Most of the attention paid to Microsoft's virtualization moves have focused on the server side, with its upcoming, virtualization-capable Windows Server 2008 and its stand-alone counterpart, Hyper-V Server.

But Microsoft is also gearing up in the desktop and application virtualization arenas, where server virtualization market leader VMware Inc. is less strong. On Tuesday, Microsoft announced a slew of moves in this space.

Microsoft is cutting the cost of licenses to do desktop virtualization with Windows Vista, and partly lifting other rules on customer companies.

Microsoft will also begin supporting customers who use its Application Virtualization technology to deliver multiple copies of Microsoft Office 2003 or 2007 to a single desktop computer at the same time.

The company also announced an alliance with longtime competitor and partner, Citrix Systems Inc., around desktop virtualization.

Finally, Microsoft has acquired a software firm with technology to improve the performance of its desktop virtualization.

Microsoft and visualization

Server virtualization involves using a hypervisor to create and run multiple virtual machines (VM) on a single server to increase efficiency and dependability.

Desktop and application virtualization also involves creating multiple VMs hosted on a single server (with an entire application stack and operating system in the desktop case, and just the application in the latter).

The difference between these two scenarios and server virtualization is that the VMs are then streamed via network to PCs or thin-client devices that execute the VMs locally. That allows applications to be more easily deployed and managed from a data center rather than installed on the local PC.

The technology is similar to Microsoft Terminal Services, where the company is actually a huge player with more than 50 million licenses sold, according to Shanen Boettcher, a general manager in the Windows client team.

Tech-wise, Terminal Services wholly hosts and executes applications from the server, resulting in slower, "paint the screen" type performance than in desktop or application virtualization.

In application virtualization, Microsoft is an emerging player, with more than 3 million seats licensed via the Microsoft's Desktop Optimization Pack (MDOP) according to Boettcher, to use either Application Virtualization 4.5 or its predecessor, SoftGrid Application Virtualization 4.2, which Microsoft acquired in July 2006.

To improve their performance, Microsoft has acquired Calista Technologies for an undisclosed amount. The company makes data compression software that, when integrated with Microsoft's virtualization and streaming technology, will enable users to get a "full-fidelity Vista Aero experience" via a virtual desktop, according to Larry Orecklin, general manager for Microsoft's System Center group.

Microsoft will also begin offering official support for customers who want to deliver Microsoft Office 2003 or 2007 to users via Microsoft Application Virtualization.

Boettcher did not know when other Microsoft applications might become officially supported under virtualization. Lack of application support has been cited as a potential deterrent to the uptake of virtualization.